Signal transmission system



Oct. 17, s 305 JR SIGNAL TRANSMISSION SYSTEM Filed Jan. 28, 1932 2 Sheets-Sheet 1 INVENTOR S 008A JR.

AT70RNEY 0a. 17, 1933. DO R 1,931,063

SIGNAL TRANSMISS ION SYSTEM Filed Jan. 28, 1932 2 Sheets-Sheet 2 m/vm ran 5. 008A JR. 8)

A TTORNEY Patented Oct. 17 1933 mission of signals andparticularly to; the control of the volume of-the-signals, 1

' One object of the invention to provide a signal transmission system that lshallin an imin a limited range before transmissionandm'x pand the signals to the original range after transs o s 1 e, i A

Another object ot the invention is to provide a systemilihat, shall compress the received slgnals before transmissionover a line and expand the transmitted signals to the original volume range, that shall control the compression of the signals by apparatus govemed according to a root of theoriginal signal sand. that shall adjust the operating characteristics of ;the vak rious parts of the system in anew and improved mannen V l 3:1

A further object or the invention isto'provide a system employing space discharge devices symmetrically connected acroesa for varying'the volume range of the. transmitted signals thatshall impress a p otential bias en, the

grids of..the devicesand'vary thebias at will to change the characteristicspf the devices and that shall impress apdtenfialfon the grids of the vices by' apparatus varying according waroot of the original volumepoi thesignals. e

In signal systems for t 'e'tfansmission of speech and radio broadcast it is alien desire able to' transmit signals an extremely wide volume range. However, signal systems are limited as to the range of volume which can satisfactorily transmitted." trans:

mission of signals hasan upper. limit to avdiddiS? tor-tion overloading line apparatus 1 such as Zrepeaters and interferenoe'w'ith othercircuii's and has. a lower limit by interferenceflfrom line noises. The .present, invention Y discloses .a system wherein the volume range of the transmitted .sig-

by a variable' gainfamplifierfin which 1 931,0 3 r mnssussroiv SYSTEM; Stephen In," New York, 1.; assignor. to'g 'reiemluimv zhbommrles lnelo 'pNew York, H.312; a e(mm :11!!! nv efiNew ot fl e H Applic ation as; 1932. strainer-mam; 1-1 1 v a q scum. (cram-.4 4i .1 a This inventionrelates to arms for the t ranss'rimmsnhemm volume: "If G mile-gain zero. It the reference-levelis'given' a value transmiss on in is masses; a wee t rated; 7

in a us- Vi the input volume in db units V some i arbitrary reference lev 1- it is desiredin' esfi e wss wm V5,: the arbitrary'referenee level;

usually the muminput v'o'liune, may ba'givm r v g The output volume .Vifrom-:the' compressor variable gain-amplifier is obtainedjmm the above 7 quations; 1",="=,v +gi= /2v. ;1 H ryer ,The empress its-m5 ead wa change th in u 101m; 1 v, ,trepimi siqe 9 incline e eordms teeth ie ve 1e 9BP.-1 t e 'c mpr sso s semiallvmnsists elf-We v variable repeats;

mu al-cen ra weenie a a a ep ises Weasel eet ems dischar WlGQS; amn sia? We ts-E h ne? a We amp fi smesi ghersfi rwa s/the a n; entral mm em rates-flames i. a re r e n (b twee vim-me direc pla ee El i including and a portion of a winding of a transformer in the line beyond the gaincontrol space discharge d liSi r; 1

.t'lh ire ti n etween he l*=,=l 1l lfi-9h ii ol \dtyfii remain my b i mined to satisfyth'e above equations. In all cases, the minimum valuo! current has been t k as about 9.4. Mila- 9TIQPQQQ19 relation betweenthe gain and thel grid pigs for each of the gain control devices may'a'lso be determined'to satisfy the' abov'e equations; From a curve plotted between grid bias and gain jog eagh of the gain control devices, the following'typical empirical equatipmmwbe'deriwd.

A c stant .biasn vre s i las uneggto the M anqvmguatiqnga s rl e ibie "(i' V p In order to'satisfyEquations (1) and (3) set forth above, the following relation is obtained:

1 w m h s.-

a a 4 a precedingthe rooter tubes may 'be' varied to promum input, then The relationship expressed "in 'Equation'- (4) must be satisfied by the'controlTcircuitIwhich governs the grid bias on the gain controldevices.

The amount of rooting required by thefrooterrin the control'circuit is indicated by the e -rponent 1/2N in'the above Equation (4).

The control circuit. which :may also. be called theiro'oter gcircuitemploys a rooter of the-type disclosedinthe patentto G. CrissQn, No. 1,737,830 and the application of N. G- Norman, Serial No.

v 5f 511,504. The rooter circuitis connected to'the transmission line "ahead of the" gain control devicesrnd comprises a linear. amplifier stage: .a' motor: or distorting device, an amplifier. anda linear; rectifier. ,The, control or rooter circuit controls the grid bias on the gain control devices toefiect a gain variation of minus one-half the volume variation at the input to the gain control devices as set forth in Equation ..'(1); :3

In-'the rooter circuit; the rooting action may jbe controlled by two factors, the impedanceof the source of el ectromotive force and the initial bias on the rooter tubes. By experiments it is round that the rootingactio'ri may-be varied by The impedance f of the "amplifier duce wide or coarsej adjustments enameinitial currents of the rooter tubes may'be' toefiect small or'fine adjustments. v i fexpander at the-receiving end of theiline is also in the form offfa' variable "gain amplifier.

, The 'expa'nderat thefreceiving end of th'e'line should be complementary to the com-pressor at the 'transmitting fend joi the 'lineso that the output volume ,V3 of the expander is equivalent to the inputvolume ot'the compressor for all values of inputovertheyworlging range. "V

Hence, if the inputvolumeof the expander is the same as the output volume V: or the 'compressor, the 'expander'output volume is 1 lfrom Equationizr V1=2Vz V where Gaiis the gainthe expander, I

. realizedtby employing alinear rectifier; infl affco'n- 'vices.

sent edf vices connected effectively in series with the transmission lineand an amplifier. The control circuit comprises an amplifier tube and a rectifier tube.

In the present system wherein the compressor reduces the volume output therefrom so that the gain variation is minus one-half the volume'variaaction is obtained by varying the bias across the rooter tubes; A fine adjustment of the gain controlfldevices in the compressor is effected by varying the grid bias obtained from the filament heating circuit for such devices.

devices ,,may alsobe adjusted by varying the resistancein the direct current platecircuit.

In the accompanying drawings Figure 1 isa diagrammatic view of the'compressor for reduc ing the volume range of I the transmitted" signals; Fig. '2 is a 'diag'rarn'rn'ati'cview of the expander for restoring the transmitted signals to the originalT'volumeran'ge,

"Referring toFig'. 1 repeater l connected in a transmission-line com- A very fine adjustment of the rooting of the drawings a variable The gain control prising conducto'r'sfl and '3 is controlled by a rooter circuit 'to reduce the volume range of the signals so that the gain variation is minus one-half the volume variation at the input to the compressor, The-variable repeater 1 comprises two sets ofigaincontrol-discharge devices 5 and 6, an amplifier 7-and a second amplifier 8.

pander 17 at the"rec'zei ving endjof thegtransmission'line; l

The gaincontrol deyices 5 and6' are connected across the-line conductors so that the volume of the transmitted signals iscontrolled according to the impedances of the devices 5 and.6.- The direct current plate 'circuitsfor the devices 5 and '6 e gtend from ,a grounded battery 18 through opposite halves of 'the primary of the transformer 14am the resistance elements 10 and12 The includingof the resistance elements 10 and 12 in the direct current plateicircuit or the gain control devices 5 and G renders' it possible to control characteristics of the" gain control devicesaby lvaryingl' the impedance elements 10 and. 12. A coarse or roughadjustment of the devices 5'and 6 is effected by-varying the resistance elements x10 and 12 The heating circuit for the filaments ofj'the gain control' device. 5 and the-amplifier 8 extends from a grounded battery 19 through a reactance 20', ballast lamp 21', filament of the amplifieritube 8, resistance element 22, filamentof the device Bland a resistance element 23 to ground. The heatin'gcircuit for the filaments of the gain controldevice 6 andfthe amplifier '7 extends from the battery 19 through .reactance 24, ballast lamp l2v5;f fiiament o f 'th'e' amplifier'tube 7,1resista'nce elerjrier'itfldifilament of the gain control device 6 andthc' resistance element '27 to ground.

grounded battery 54 7 The resistance elements 23 and 27 in the Ilia: mentheating circuits for the devices 5 and 6 serve to provide potential drop'for impressing a poten? 23 and '27. Abattery 28 normally impressesa.

biasing'potentialonthe grids of'the devices 5 and '6 and the adjustable resistance) elements-23 and 27 serve as means toadjust. the potential on the grids in accordance with operating conditions. The resistance elements 23 and 27 may be "adjusted to compensate for variations in the voltage of the batteries 28," 18 andy19 and maybe varied to ad-just'the characteristics of the gain control devices to 'ag'ree withthe operation of the rooter circuit to be de scribed. The resistance elements 22 and 26- arecomplementary to the resistance elements 23 and 27 andareyariedin' accordance with the variation of resistance-elements 23 and 27 so thatthere will 'be noyariation in theheating current when "any adjustment is made'in the grid-biasof devices 5 and 6. 3 Y

A battery 31 isprovided for impressing a biasingipotentialfon the grids of-the two amplifier tubes 7 and 8. A battery 32 suppliesplatepotential throughthe choke coils 33' and 34, for the amplifier tubes 7 and 8. 'Thec'ond'ensers 35' and 36 serve as by-pass condensers. I

The control or rooter circuit- 4 impresses a variablepotential-onthe grids of the gaincontrol devices '5' and 6m order to 'vary-thegain of the devices so'thatthe transmitted signals have 'a volume range of "one-halt the volume of the signals as received. -The rootercircuit comprises an amplifier 38, a'rooter 39, anamplifier40and' a rectifier '41. The amplifier 38 is a' space'discharge tube of the four-element typehaving the input circuit thereof connected by a transformer 42 to a potentiometer 45. The potentiometer 43 is connected across the line'conductors2 and 3 before the transformer 13. The output circuit of amplifier 38 is connected by a transformer 48 to the rooter39. The rooter 39 "comprises two fourelement space discharge tubes49 and 50 having the grids and plates of each tube directly' connected together. The rooter 39 is directly connectedto the amplifier 40 which is inthe form of a four-element spacedischarge device. The out put circuit of the space dischargedevice 40: is connected by a transformer 51 to the rectifier 41 which" is in the form of a four-element space discharge tube having the plate and grid thereof connected together. The rectifier 4115 connected through a filter 52 togrounded resistance me, merits 53; Grid bias fromthe resistanceel'ement 99 for the tube'41 prevents any variations in grid bias on the devices 5 and 6 when the input volume fallsb'elow a predetermined level; :The potential drop across a portion of the resistancefelements 53' is the potential impressed on the gridsofthe operation of the compressor.- The filter 52 serves to smooth out ripples in the potential supplied by the rectifier 41"to the grids of "the gaincontrol devices 5 and 6." Y T' Th'e heating elements of the amplifierjtubes 38 and 40, the rooter tubes 491 x1650 and the rec tifier tube 41 are supplied-'withcurrent from a Plate potential for the 1 amplifier tubes 38 and 46 is supplied by'a grou'nd ed battery 55, suitable by pass condensers 56 and 57 being connected -to ,th e plate circuits of the p i r er iss rov d diar imp e s:

gain 'control devices 5 and 6 for eont'rollingthe ing! a biasing potential on: 'thef grid'of the amplifier tube 38. i

Resistance elements 60 'and 61- are provided for adjusting the biasing potential across the rooter tubes 50'*and 49.:. It willube noted that the resistanceelements 60 and 61 are connected across the heatingelem'ents forl'the rooter/tubes and that the circuitscompleted throughrthe rooter tubes resistance elements60 and 61 permitaa very fine adjustment of. the rooting action. Therooter tubes have'been described in detail in the Crisson Patent1,737,830 dated Deeemberii, 1929 anda detailed? description here is deemed unnecessary.

The expander 17: .at the-receiving endof the transmission line comprisesgavariable repeater 62 and .a'control circuit: 63. The expander serves to restore the" volume: range orthe received signals to their original range before-they were acted. ontby the compressor. Asset forth before the .gain effected by the variable repeater- 01" the expander willlbe equal'to the-output volume of the compressor at the. transmitting end 'Of' '.the line" :i.1::-.: i g

" The :variable repeater comprises twoqgain controlidevices' 64 and 65in the formiof-three-ele- .me'nt space" discharge tubes. The tubes 64 and'65 .areiefiectively. connected in series with the trans- 'missionline; the: input'circuits of thetubes 64 and 65 being connectedsto atransformer '66 in the line. and: the output circuits. of the tubes 64 and.65 being connected by a transformer v67 to an amplifier 68 in the form of a threeelement space discharge; device. The' output circuitxof I the amplifier tube 68:is connected to the trans-v former'69."'

1 1 Grid bias' for the gain. control devices64 1 and,

65 is supplied by a battery 70 andv by th'e'drop across resistance elements 'Zl'a'nd '72 included in I tential forthe gainicontrolzdev'ices 64 and'65 is supplied 'byiaa'grounded.batterya75 through resistance elements f7 6 and 77% and 2 the primary winding'loi'tthe: transformer '67. 1 Condenser" 30 actshas ansAQCQ by-pass across resistance elementsi76"and 77. vPlatel potential-fora the amplifieritube '68'is supplied 'from'a ground battery tentialaon thegridsof" the gain: controladevices 64 and-'65 comprises.apotentiometer 81 connected acrossthe transmissionline ahead -'of thelwtransq former 66. :-An' amplifier 84 inrthe form of a three-element space discharge. tube-has its input circuit connected' by:a1transformer 85 across a portion of-..-the. potentiometer 81; The output circuit of the amplifier 84. is connected 'by transformer 86 toa'rectifier187. The rectifierr87 is connecteditoa filter 88 anda potentiometer 89.

Part oft-he potential [dropacross the .potential 89 issuppliedto thefgrids of the gain jCOIitIOl devices 64 and 65. The rectifier 87 is inthe form of a four-element space discharge device havingthe grid and plate connected together. The amplifiertube 84 is supplied with plateipotential from a battery through a' choke coil.9l.. A battery 92 is provided for supplying current to the heating element of the rectifier B'Tandzfor sup-V.

plying filamentlcurrent .to theamplifier 84, amplifier 68 and the filaments of thesgainacontrol devices 64 and 65. The battery 80 which supplies grid bias to the amplifier tube 68also supplies grid biasing potential to the tube 84. l

In .a system constructedas heretofore described the volume range. of signals is reduced by the compressor due to the fact that the gain variation producedby the compressor is minus one-half the. volume variation of the input to the compressor. The control of the compressor is 'eflectedby a rooter of the type disclosed in the above mentioned Crisson patent. In order to efiect operation of the compressor so, as to effect compressionofthe signals'in ar-fixed relation or in accordance with the fixed equation it is necessary to efiect'accurate adjustment of the rooting operation as well as the operation of the gain control devices. Means was disclosed whereby the operation of the rooting or the controlling circuit and the operation of the variable repeater may be adjusted quickly, and withpre-.

cision. Furthermore, the variable gainiof .control' devices in the compressor and in the expander are symmetrically connected to the linesoas not to needlesslyinterfere with the transmission of signals. I

Modifications in the system and-in the arrangement and locationof the parts may be made with?- in the spirit and scope of the invention and such modifications are intended to be covered in :the

appended claims.

7 'What is claimed'is: j I

adjustable grid biasing resistance therein, means for adjusting the drop across said, resistances impressed on the grids of 'said'devices to vary-the constant bias on said grid,.and means for autoe matically varying the potential .on the-gridsof said devices according to a; root of the volume of the signals supplied to the transmission channel; 2. In a signal system, a transmission channel, impedance elements symmetrically placed in op.- posite sides of thetransmission channeL'a trans-l former connectedin the. transmission channel beyond the impedance elements, two" three-"element space discharge devices connected across the transmission channel between said impedance elements withthe direct plate current path of each of the devicesincluding oneof .sa'id impedance elements and a portion of one winding of said transformer, means for impressing a bias ,on thegrids of said devices from the filament heating circuit of said tubes and for. varying the bias impressed on the grids of the devices" without varying the heating of the'fllaments, and means for automatically 'varying the potential on the grids of said devices accordingto a root of the volume of the signals supplied to the transmis sion channel; 7

-13; In'a signal system; a transmission channel, impedance elements symmetrically placed in 0p: posite sides of the transmission channel, two three-element space discharge devices connected across the transmitting channel between said 80 impedance elements to shunt the signal current according to the impedances of the tubes, means comprising two spacedischarge tubes, each hav I ing a filament,-a heating element and an anode for automatically controlling the grid potentials of vsaid three-element space discharge devices according to aroot of the volume of the signals supplied to the transmission channel, means employing the resistanceof saidv heating elements for placing a constant bias across said space discharge tubes, and-means for impressing adjustable potentials across said space discharge tubes from the circuit of said heating elements.

4. In a signal system,a-transmission line, two three-elementspace discharge devices connected across the transmitting channel to shunt the signal current and control the volume of the signals according to the impedances of thedevices, means comprising two space dischargev tubes for automatically controllingthe'grid potentials of said three-element space-discharge devices according to'a root ,of the volume of the signals supplied to the transmission channel, and means for impressing an adjustable potential bias on eachof said space dischargetubes. p

, 5. In asignal system, a transmission line, two three-element'space discharge devices connected across said line to shunt the transmitted signals and control-the volume of the signals according tothe impedancesoi the tubes, means comprising 11 two space discharge tubes forcontrolling the grid potentials of saidthree-element space discharge devicesaccordingto a root of the volume of the signals supplied to the-line, means for impressing an adjustable potential on each of said space dis- 1115 chargetubes for controlling the characteristics thereof, meanscomprising two three-element expanderutubes connected effectively in series with said line atthe receiving end, thereof, and means for controlling the potential on the grids of said I expandertubes according to the volumeoi: the signals received by the expander to control the expander tubes and restore the signals to the original'volume. r r a,

6.-In a signal system, a transmission line, two threeeelement space discharge devices connected across said line to :control the volume of the signals according to the impedances of, the tubes, means for controlling the grid potentials of said devices according, to a root of the volume of the signals suppliedto the'line, means comprising two three-element expander tubes connected symmetrically and effectivelyin series with said, line at the receiving end thereof, and means for controlling the potential on the grids of said I35 expander tubes according ,to the volumeof the signals received by the expander to control the connected symmetrically and effectively inseries with the li'ne at the receiving end thereof, for restoring the signals to the originalvolume.

8; In a signal system, a transmission line, threeelement space discharge devices connected across said line for controlling the volume of the transmitted signals according to the impedances of tentials of said devices according to a root of the volume of the signals supplied .to the line, means comprising three-element expander tubes connected symmetrically and efiectively in series with the line at the receiving end thereof for restoring the signals to the originalvolume; and means for adjusting the characteristics of said expander tubes by impressing potential on the grids thereof from the filament heating circuit. 7

9. In a signal system, a transmission line, threeelement space discharge devices connected across the line for controlling the volume of the trans mitted signals according to the impedances '01 the devices, means comprising space discharge the devices, means for controlling the grid po- 7 for restoring the signals to the original volume v p Q s'mrmm noBA, J83 

